Velux Or Roof Window Leaking

What's happening?

A roof window sits in a hole in the roof, sealed to the tiles by a flashing kit that sheds water around it. It leaks in a few predictable ways. Water gets past the flashing at the lower corners, where it is thickest. Water is blown under the top or sides in wind-driven rain. A seal or gasket at the bottom of the sash has hardened or collected debris. The pitch is too low for the flashing type fitted. Or the window was fitted poorly, recessed too far or without the underlay lapped into the gutter. Many reports are not leaks at all: condensation forming on cold glass or a cold frame runs to the bottom and looks the same. Opening the window after rain and looking at where the wet starts helps tell them apart.

What usually causes it?

• A flashing kit that was fitted wrongly or has been disturbed, especially at the bottom corners
• A pitch lower than the flashing and window are rated for
• Wind-driven rain blown under the top or sides of the frame
• Debris or moss packed against the lower flashing so water backs up
• A hardened or worn seal or gasket
• A missing or badly lapped underlay collar around the frame
• Condensation on the glass or frame, mistaken for a leak

Is it dangerous?

Low as a leak, but water running into the lining rots timber and stains the ceiling. Do not climb onto the roof to look: roof windows sit on a slope and the glass and flashings are slippery. Switch off any lights wet from above.

Can I fix it myself?

Wipe the glass and frame dry, then check after rain whether the wet reappears on the glass (condensation) or on the lining and corners (leak). Clean the seal and check for debris by looking from inside and from a safe position outside. Do not seal around the frame with silicone: it hides the path and traps water. Check that trickle vents or the window's own ventilation are not shut.

When should you call a roofer?

Call a roofer or the window's installer if wet appears on the lining or at the corners in rain, if the leak is new after fitting, or if wet appears in heavy or windy rain. VELUX publishes help for leaking windows, and an installer with the manufacturer's guarantee should be asked first.

What will the roofer actually do?

• Check whether the water is leakage or condensation by inspecting the frame and lining
• Inspect the flashing kit, the underlay collar and the seals
• Check the roof pitch and window position against the manufacturer's limits
• Re-dress or replace the flashing and clean or replace the seal
• Re-lap the underlay and test with water before leaving

Who fixes this

• Roof leak repair
• Roof window installation
• Lead flashing repair

Questions people ask

Sources & References

1. VELUX: help and advice
2. NFRC: choosing a roofing contractor
3. HSE: roof work